A good number of functions or features, be it in the automobile sector or in other fields, require systems making it possible to have positioning that is servo-controlled in rotation or in translation, it being possible for such systems to be of the pneumatic, hydraulic, or electric types. In the context of the present invention, consideration is given to electric actuators only. In this invention, the term “actuator” describes the assembly formed by an electric motor, by any detection means for detecting the position of the motor rotor, by any movement transformation means, by an outlet position sensor, by the commutation electronics, and by the connector.
Two main families of actuators can be identified:                “dumb” actuators; FIG. 1 shows such an actuator (2), which includes a brushed DC motor (20) and a position sensor (7) that can be summarized as being a resistive track associated with a slider; the smart portion in charge of position servo-control is in a separate, offset electronic unit (1), known as the electronic control unit or “ECU” by persons skilled in the art; and        “smart” actuators; such an actuator includes a microcontroller in charge of the position servo-control function; generally, this type of actuator is controlled either by a pulse-width modulation (PWM) signal or by a local interconnect network (LIN) or controller area network (CAN) communication bus, those types of bus being recognized as standard buses in the automobile industry.        
For automatable applications close to the internal combustion engine, such as, for example, wastegates of a turbo system, the “dumb” solution is much preferred to the “smart” solution for reasons of high-temperature compatibility of the electronic components, in particular of the microcontroller. In a dumb solution, as shown diagrammatically in FIG. 1, an ECU (1) reads the position signal delivered by a position sensor (7) coupled to the mechanical outlet (12) of the actuator (2), and then computes a torque and direction signal (6) applied to a brushed DC motor (20). The mechanical outlet (12) is coupled to an external member (not shown) to be moved, such as a valve member or a needle, for example. The action on the motor (20) is transmitted to the mechanical outlet (12) of the actuator (2) via a gearing stage or (rotary-to-linear) movement transformer (9). Thus, this closed loop makes it possible to servo-control the mechanical outlet (12) of the actuator (2) in terms of position. There are few connections (3) between the ECU (1) and the actuator (2): 2 wires for the brushed DC motor (20)—for which the differential signal between the two wires can be a positive signal or a negative signal—and 3 wires for the position sensor (7)—including one for ground, one for a positive signal for the power supply, and one for the position signal. The DC motor (20) responds to the torque and direction signals (6) delivered by the ECU (1) through a power bridge referred to as an “H-bridge” (see FIG. 24) constituted by four transistors (15a, 15b, 15c, 15d).
U.S. Pat. No. 5,773,941 describes an invention making it possible to control, in one direction, a three-phase brushless DC motor using two wires, one of which is a reference (ground or OV) wire and the other which is a torque signal wire. An external power supply delivers the torque signal that can be a continuous signal or a chopped signal. The commutation electronics 20 is self-powered by a rechargeable power supply taking its energy from the torque signal.
Regardless of the industrial or automobile applications, the brushless DC motor is currently in widespread and preferred use because of the advantages it offers compared with the conventional DC motor as described in U.S. Pat. No. 4,365,187 (column 1, line 9). The preferred type of brushless motor is the one having a single-phase brushless DC motor structure with one coil or two half-coils. Simple electronics that can be integrated in the vicinity of the motor, or indeed in the housing 30 of the motor, manages the self-commutation of said motor on the basis of the signal delivered by one or two Hall-effect probes.
The increasing electrification of the functions present under the hood or bonnet of an automobile is resulting in the electrical actuators having to cope with various constraints and stresses that are increasingly severe, in particular as regards withstanding ambient temperatures greater than 125° C. Existing “smart” systems, incorporating a microcontroller and/or complex electronics necessary for controlling a motor and for servo-controlling the position of the actuator, are limited in terms of the ambient temperatures they can withstand. The type of component that is economically “viable” does not make it possible to go beyond the limit of 125° C., and often requires costly cooling means.
The existing “dumb” systems are compatible with the desired ambient temperatures because the actuator does not include any complex and sensitive electronic component. However, such an actuator uses a brushed DC motor that, industrially speaking, offers lower performance and is less compact than a brushless DC motor, which also offers the huge advantage of having a lifespan that is much longer than the lifespan of a conventional brushed DC motor. It is accepted by persons skilled in the art that brushed DC motors are sources of electromagnetic disturbance, which is a sensitive point in an environment that is increasingly occupied by electronic systems and computers.
One of the conventional structures for polyphase brushless DC motors is a motor having three phases connected either in a star configuration or in a delta configuration, thereby leaving three connection points for the power supply of the motor. The self-commutation of a brushless DC motor for a positioning application requires three probes to be used to determine the position of the motor rotor. Designing a “dumb” actuator with a brushless DC motor, instead of a brushed DC motor, requires use to be made of an ECU that is adapted and designed for controlling a three-phase motor, namely a three-phase bridge with six transistors and five connection points with rotor probes. Position servo-control systems require both-way control of the rotation of the motor, which cannot be achieved by the invention described in U.S. Pat. No. 5,773,941, in which the inlet (referenced 22 in that text) accepts one polarity only.
The other applications of brushless DC motors, the majority of which are single-phase, such as those described in U.S. Pat. No. 4,365,187 are mainly used for fans or pumps requiring only one rotation direction. As described in column 5, line 3 of the above-mentioned patent, the structure of the motor, by its geometrical shape or by the positioning of the probes, should be designed to ensure that the motor starts properly and in the preferred direction of rotation. As a result, the single-phase brushless DC motor and its control electronics are not suitable for positioning applications, which are the subject of the present invention, unceasingly requiring position correction that needs the motor to be rotated in both directions.